. SUMMER INDUSTRIAL TRAINING REPORT on STEEL PRODUCTION PROCESS at BOKARO STEEL PLANT - SAIL Ankit Gourav (5912161) USN – 1SI12EE007 1
Dec 09, 2015
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SUMMER INDUSTRIAL TRAINING REPORT
on
STEEL PRODUCTION
PROCESSat
BOKARO STEEL PLANT - SAIL
Ankit Gourav (5912161)
USN – 1SI12EE007
IV Semester Electrical and Electronics Engineering
Siddaganga Institute of Technology, Tumkur
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CERTIFICATE
This is to certify that the project entitled “STEEL PRODUCTION
PROCESS” at SAIL- BOKARO STEEL PLANT has been carried out by
Mr. Ankit Gourav from 30th June 2014 to 9th August 2014, under my
supervision in partial fulfilment of his BE, Electrical and Electronics
Engineering course at Siddaganga Institute of Technology, Tumkur
I am satisfied with his sincere performance and study conducted by him in
SAIL-BOKARO STEEL PLANT. The project is hereby approved as a
bonafied work carried out and presented in a manner satisfactory to its
acceptance area to the Electrical and Electronics Enginnering for which it
has been submitted.
I recommend submitting the project report. I wish him all success in life.
This is also certified that the project work is original and has not been submitted
to any other place.
Project Guide
Mr. Rajendra Kumar
Jr. Manager - HRD
Bokaro Steel Plant
Date: 8th August 2014 SAIL
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ACKNOWLEDGMENT
I am highly obliged to Mr. Rajendra Kumar -Junior Manager, HRD
SAIL-BSL, my prime internal guide for his invaluable support, guidance and
knowledge that he shared with me thereby aiding me in making this project a
success along with different guides of each sections who provided their utmost
working knowledge, which has broaden my area of interest and benefited
mostly in completing the project. Their guidance and suggestions was always
there without which it was a difficult step to complete the project alone.
This training provided me some experience not only in practical aspects
of industry but also in human relation, group work , individual work and
provided great insights into the actual working of an industry.
I hereby also declare that the contents in the report are true to the best of my
knowledge.
Lastly I thank faculty and staff members of Siddaganga Institute of Technology,
Tumkur and Bokaro Steel Plant –SAIL which gave me an opportunity
regarding training purpose and helped me in building some experience in my
career.
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DECLARATION
I hereby declare that the following documented project report titled
“STEEL PRODUCTION PROCESS" is an authentic work done by me
as a part of my industrial training in Bokaro Steel Plant, SAIL.
I also further state that the project has been prepared by my own with the
secondary data provided in the reports of the company, which were
essential for the completion of the project. The project was undertaken as a
part of the course curriculum of BE, Electrical and Electronics
Engineering .
Ankit Gourav
(5912161)
1SI12EE007
SIT, Tumkur
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Table of Contents1 COMPANY PROFILE............................................................................................................6
1.1 BACKGROUND & HISTORY..................................................................................8
1.2 SAIL Today.................................................................................................................9
1.3 BOKARO STEEL PLANT.......................................................................................12
2 RAW MATERIAL HANDLING PLANT............................................................................14
2.1 Introduction....................................................................................................................14
2.2 Different Raw Materials.................................................................................................16
2.3 Material Handling Equipments.......................................................................................16
2.4 Customers of RMHP......................................................................................................18
2.5 Benefits of RMHP/OHP/OB&BP..................................................................................19
3 COKE OVEN & COAL CHEMICALS................................................................................20
3.1 Introduction....................................................................................................................20
3.2 Types & Sources of Coking Coal...................................................................................21
3.3 Coal Handling Plant.......................................................................................................21
4 BLAST FURNACE..............................................................................................................24
4.1 Introduction....................................................................................................................25
4.2 Blast Furnace and Accessories.......................................................................................26
4.3 Zones in Blast Furnace...................................................................................................26
4.4 Hot Blast Section............................................................................................................27
4.5 Cast House......................................................................................................................28
5 STEEL MAKING.................................................................................................................31
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5.1 Introduction....................................................................................................................31
5.2 Hot Metal Desulphurisation...........................................................................................32
5.3 Open /Twin Hearth Furnaces..........................................................................................33
5.4 Basic Oxygen Furnace (BOF)- LD Converter................................................................33
6 CASTING.............................................................................................................................36
6.1 Introduction....................................................................................................................36
6.2 Casting Preparation........................................................................................................37
6.3 Casting Process...............................................................................................................38
7 OTHER FACILITIES...........................................................................................................40
7.1 Steel Melting Shops........................................................................................................40
7.2 Continuous Casting Shop...............................................................................................41
7.3 Slabbing Mill..................................................................................................................41
7.4 Hot Strip Mill.................................................................................................................42
7.5 Cold Rolling Mill...........................................................................................................42
7.6 BOKARO STEEL PLANT - PRODUCT BASKET......................................................43
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1 COMPANY PROFILE
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STEEL Authority
OF INDIA LIMITED
Satisfaction Customer
Aspiration Unlimited
Improvement Continual
Leadership Market
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Steel Authority of India Limited (SAIL) is the leading steel-making company in India. SAIL is India's largest steel producing company with a turnover of Rs. 47,042 crore,
SAIL is among the five Maharatnas of the country's Central Public Sector Enterprises. It is a fully integrated iron and steel maker. SAIL manufactures and sells a broad range of steel products that are used for different purposes like domestic
construction, engineering, power, railway, automotive and defence industries and for sale in export markets. Since its inception, SAIL has been instrumental in laying a sound infrastructure for the industrial development of the country. Besides, it has immensely contributed to the development of technical and managerial expertise. It has triggered the secondary and tertiary waves of economic growth by continuously providing the inputs for the consuming industry.
1.1 BACKGROUND & HISTORY
After independence in the formative years of an emerging nation – India, the builders of modern India worked with a vision - to lay the infrastructure for rapid industrialization of the country. The steel sector was one amongst which to propel the economic growth. Hindustan Steel Private Limited was set up on January 19, 1954. The President of India held the shares of the company on behalf of the people of India.
Hindustan Steel (HSL) was initially designed to manage only one plant that was coming up at Rourkela. For Bhilai and Durgapur Steel Plants, the preliminary work was done by the Iron and Steel Ministry. From April 1957, the supervision and control of these two steel plants were also transferred to Hindustan Steel. A new steel company, Bokaro Steel Limited, was incorporated in January 1964 to construct and operate the steel plant at Bokaro.
The Ministry of Steel and Mines drafted a policy statement to evolve a new model for managing industry. The policy statement was presented to the Parliament on December
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2, 1972. On this basis the concept of creating a holding company to manage inputs and outputs under one umbrella was mooted. This led to the formation of Steel Authority of India Ltd. The company, incorporated on January 24, 1973 with an authorized capital of Rs. 2000 crore, was made responsible for managing five integrated steel plants at Bhilai, Bokaro, Durgapur, Rourkela and Burnpur, the Alloy Steel Plant and the Salem Steel Plant. In 1978 SAIL was restructured as an operating company.
1.2 SAIL Today
SAIL today is one of the largest industrial entities in India. Its strength has been the diversified range of quality steel products catering to the domestic, as well as the export markets and a large pool of technical and professional expertise.SAIL produces iron and steel at five integrated plants and three special steel plants, located principally in the eastern and central regions of India. The company also owns iron ore, limestone and dolomite mines: domestic sources of raw materials. These mines are situated close to the eastern and central regions of India giving company competitive advantages. The company has the distinction of being India’s second largest producer of iron ore and of having the country’s second largest mines network.
MAJOR UNITS
Major units of SAIL consist of integrated Steel plant, special steel plant & subsidiary units.
Integrated Steel Plants
Bhilai Steel Plant (BSP) in Chhattisgarh
Durgapur Steel Plant (DSP) in West Bengal
Rourkela Steel Plant (RSP) in Orissa
Bokaro Steel Plant (BSL) in Jharkhand
IISCO Steel Plant (ISP) in West Bengal
Special Steel Plants
Alloy Steels Plants (ASP) in West Bengal
Salem Steel Plant (SSP) in Tamil Nadu
Visvesvaraya Iron and Steel Plant (VISL) in Karnataka
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Subsidiary
Maharashtra Elektrosmelt Limited (MEL) in MaharashtraJoint Ventures
NTPC SAIL Power Company Pvt. Limited (NSPCL)
Bokaro Power Supply Company Pvt. Limited (BPSCL)
Mjunction Services Limited
SAIL SCL Limited
SAIL-Bansal Service Centre Limited
Bhilai JP Cement Limited
Bokaro JP Cement Limited
SAIL & MOIL Ferro Alloys (Pvt.) Limited
S & T Mining Company Pvt. Limited
International Coal Ventures Private Limited
SAIL SCI Shipping Pvt. Limited
SAIL RITES Bengal Wagon Industry Pvt. Limited
Today, the accent in SAIL is to continuously adapt to the competitive business environment and excel as a business organization, both within and outside India.
SAIL - Into the Future
Modernization & Expansion
SAIL, is in the process of modernizing and expanding its production units, raw material resources and other facilities to maintain its dominant position in the Indian steel market. The objective is to achieve a production capacity of 26.2 MTPA of Hot Metal from the
base level production of 14.6 MTPA (2006-07 – Actual).
Orders for all major packages of ISP & SSP and part packages of BSL, BSP, RSP & DSP Expansion
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have been placed and these packages are in various stages of implementation. Objective of Expansion Plan is to expand the production. The production target of hot metal, crude steel and saleable steel after Expansion is indicated below:
(Million tonne per annum)
Item Base Case(2006-07)
Actual
After Expansio
nHot Metal 14.6 26.2 (23.5)
Crude Steel 13.5 24.6 (21.4)Saleable Steel 12.6 23.1 (20.2)
Plant-wise Capacity Envisaged After Expansion (Mtpa)
Plant Hot Metal Crude Steel Saleable Steel
BSP 7.5 7.0 6.53
DSP 3.5 3.0 2.83
RSP 4.5 4.2 3.8
BSL 7.44 7.00 6.53
ISP 2.91 2.5 2.37
SSP - 0.18 0.34
ASP - 0.48 0.43
VISL 0.33 0.23 0.22
Total 26.18 24.59 23.13
The investment for modernization and expansion programme of SAIL is estimated at about Rs.54,333 crores.
1.3 BOKARO STEEL PLANT
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Bokaro Steel Plant - the fourth integrated plant in the Public Sector - started taking shape in 1965 in collaboration with the Soviet Union. It was originally incorporated as a limited company on 29th January 1964, and was later merged with SAIL, first as a subsidiary and then as a unit, through the Public Sector Iron & Steel Companies (Restructuring & Miscellaneous Provisions) Act 1978. The construction work started on 6th April 1968.
The Plant is hailed as the country’s first Swadeshi steel plant, built with maximum indigenous content in terms of equipment, material and know-how. Its first Blast Furnace started on 2nd October 1972 and the first phase of 1.7 MT ingots steel was completed on 26th February 1978 with the commissioning of the third Blast Furnace. All units of 4 MT stage have already been commissioned and the 90s' modernization has further upgraded this to 4.5 MT of liquid steel.
Bokaro is designed to produce flat products like Hot Rolled Coils, Hot Rolled Plates, Hot Rolled Sheets, Cold Rolled Coils, Cold Rolled Sheets, Tin Mill Black Plates (TMBP) and Galvanized Plain and Corrugated (GP/GC) Sheets. With the completion of Hot Strip Mill modernization, Bokaro is producing top quality hot rolled products that are well accepted in the global market. Bokaro has provided a strong raw material base for a variety of modern engineering industries including automobile, pipe and tube, LPG cylinder, barrel and drum producing industries.
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2 RAW MATERIAL HANDLING
PLANT
2.1 INTRODUCTION
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Raw Material Handling Plant or Ore Handling Plant or Ore Bedding and Blending Plant
play a very important role in an Integrated Steel Plant. It is the starting point of an
integrated steel plant, where all kinds of raw materials required for iron making/steel making
are handled in a systematic manner, e.g., unloading, stacking, screening, crushing, bedding,
blending, reclamation, etc.
Different types of major raw materials used in an integrated steel plant are
Iron Ore
Lime stone
Dolomite
Manganese Ore
Ferro and Silica manganese
Quartzite and Coal
For Blast Furnace route Iron Making the main raw materials required are-
Iron ore lump
Blast furnace grade lime stone
Blast furnace grade dolomite
Coke
Sinter
Scrap
LD Slag
Mn Ore
Quartzite
The main objective of raw material handling plant/ore handling plant/ore bedding and
Blending plant is to:
Homogenize materials from different sources by means of blending
Supply consistent quality raw materials un-interruptedly to different customers
Maintain buffer stock
Unloading of wagons/rakes within specified time norm
Raw material preparation (like crushing , screening etc.).
The main functions of RMP/OHP/OB&BP are –
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Unloading& stackingof raw materials,
Screening of iron ore lump & fluxes,
Crushing of coke/flux and base mix preparation,
Dispatch of processed inputs to customer units
2.2 Different Raw Materials
1. Iron Ore Lumps
2. Iron Ore Fines
3. BF grade Lime
4. BF grade Dolomite
5. SMS grade Limestone
6. SMS grade Dolomite
7. Manganese Ore
8. Mixed Breeze Coke generated inside the plant (Blast Furnace & Coke Ovens)
9. Mill Scale Generated inside the plant
10. Flue dust Generated inside the plant
11. LD Slag Generated inside the plant
Right quality raw material is basic requirement to achieve maximum output at lowest
operating cost. Quality of raw materials plays a very important and vital role in entire steel
plant operation. Quality of raw materials (incoming) and processed material (outgoing) is
monitored by checking the incremental samples collected from the whole consignment
samples are collected at Auto Sampling Unit or Sampling Unit. The samples prepared after
quarter and coning method are sent for further analysis.
2.3 Material Handling Equipments
Sl No.
Major Equipments Main Function
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1 Wagon Tippler For mechanized unloading of wagons
2 Car Pusher For pushing the rakes inside the wagon tippler
3 Track Hopper For manual unloading of wagons
4 Stackers For stacking material and bed formation
5 Barrel / Bucket wheel For reclaiming material also called blenders
6 Transfer Car For shifting equipments from one bed to another
7 Screens For screening to acquire desired quality material
8 Crushers For crushing to acquire desired quality material
9 Belt Conveyors For conveying different materials to the destination
The material such as IOL, IOF, Lime Stone, Dolomite, etc, unloaded in wagon tippler or
track hopper is being conveyed through the series of belt conveyors to the designated bed and
stacked there with the help of stackers. Bed formation takes place by means of to and fro
movement of stacker. Number of optimum layers in a bed is controlled by stacker speed.
Number of layers in a bed determines the homogeneity of the bed and is reflected in standard
deviation of final bed quality. More is the number of layers; more is the bed homogeneity and
lower the standard deviation.
Blending is the mechanized process of stacking & reclaiming to get optimum result in
physical & chemical charecteristics of raw material,this means that blending is a process of
homogenization of single/different raw materials over a full length of
pile/bed.Homogenization increases rapidly as the no of layers exceeds 400 & the effect goes
on decreasing after 580 layers.
Iron Ore Lump Screening :
Screening of IOL is necessary because IOL coming from mines contains lot of undersize
fraction (-10 mm.), which adversely affects the blast furnace operation. Therefore, this
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undersize fraction (fines) is screened out at IOL screening section and then stacked in the
designated IOL beds, from which this screened ore is supplied to blast furnace.
Base Mix Preparation :
In some plants, base mix or sinter mix or ready mix for sinter is being prepared at
RMHP/OHP/OBBP for better and consistent quality sinter and also for increasing sinter plant
productivity. Base mix is a near homogeneous mixture of IOF, crushed flux, crushed coke,
LD slag fines, mill scale, flue dust, etc, mixed at certain proportion.
Flux:
Flux is a mixture of Lime Stone and Dolomite in certain proportion required in sinter-
making. Fraction of (-3mm.) in crushed flux is 90% and more. The main function of flux is to
take care of gangue in blast furnace and also to increases the rate of reaction to form the good
quality slag. Flux acts as a binder in sinter making to increase the sinter strength.
Rod mill or hammer crusher are used for crushing Limestone & Dolomite Lumps to required
size i.e., (-3mm.) > 90%.
Coke Breeze:
Another important ingredient in base mix is crushed coke of size fraction (-3mm.) 85 %.
( Minimum) Coke for base mix preparation is received from coke ovens and blast furnace,
called mixed breeze coke. The size fraction ( + 12.5 mm.) is screened out and sent along with
sinter to blast furnace as a nut coke. The under size material is crushed in the two stage roll
crusher i.e. primary and secondary roll crusher to achieve requisite size fraction of (-3mm.)
85%.
2.4 Customers of RMHP
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Sl. No.
Customer Product/ Material
1 Blast Furnace Size Ore or Screen Iron Ore Lump
2 Sinter PlantMix or iron ore fines, crushed Flux, dolomite fines & crushed coke, nut coke
3 Calcining/ Refractory Plant SMS grade Limestone & Dolomite
2.5 Benefits of RMHP/OHP/OB&BP
Provides consistent quality raw materials to its customer and also controlling the cost by:
Minimizing undersize in iron ore lump & flux by means of screening
Consistency in chemical & physical analysis by means of bedding & blending
Input quality over a time period is known
Metallurgical waste utilization
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3 COKE OVEN & COAL
CHEMICALS
3.1 Introduction
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Coke making is the process to convert coking coal, through a series of operations, into
metallurgical coke. The process starts from unloading of the coal at the wagon tipplers &
ends at sizing & transportation of coke to Blast furnace.
Formation of Coal:
The plant & vegetations buried under swamp bottom during earthquakes or due to other
environmental changes were subjected to heat & pressure. During the initial period plants &
vegetations decay to form peat. Over a long period of time water is forced out due to
tremendous pressure of the overburden & due to heat generation, converting the mass to
LIGNITE. Continuous compaction & ageing converts the Lignite to Bituminous coal. This
process takes million of years.
3.2 Types & Sources of Coking Coal
All coals are not coking coals, i.e. all types of coal can’t be used for coke making. Coking
coals are classified as:
Prime Coking Coal (PCC)
Medium Coking Coal (MCC)
These are generally known as Indigenous coal, i.e. available in India. In addition to the above
coking coal the following types of coal are also used for coke making in all SAIL plants.
Imported Coking Coal (ICC) – Hard
Soft Coking Coal (SCC)
Coal is extracted from coal mines & processed in the coal washeries to lower down the ash
content to make it fit for coke making.
3.3 Coal Handling Plant
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Coke is one of the most important raw materials used to extract iron from the iron
ore.
The success of Blast Furnace operation depends upon the consistent quality of coke,
which is used in Blast Furnace. The quality of coke depends upon the pre-
carbonisation technique, carbonization & post-carbonisation techniques used in Coke
ovens. Pre-carbonisation technique is controlled by Coal handling Plant.
Unloading & lifting of coal:
Washed coals from washeries are received at the Coal Handling Plant by Railways
wagons. Generally 58 wagons, called a rake, are brought to the plant at one time.
These wagons get unloaded in wagon tipplers. Here the wagons are mechanically
clamped & turned through 180° to 360° to discharge the coal onto down below
conveyors. Then through a series of conveyors the coal is stacked in coal yard through
a Stacker. The coal yard is divided into separate segments where different types of
coal can be stacked in respective earmarked areas. It is very important to stack
different types of coal separately so as to avoid mix up of two types of coal. Mix up of
coal is highly detrimental for coke making. From the coal yard, coal is reclaimed
through Reclaimer & by a series of conveyors gets transported to either crushers or silos
as per prevailing system in different SAIL plants.
Crushing & Blending:
The sequence of crushing & blending is different in different SAIL plants. The system
of crushing the coal & then blending is followed is RSP where as blending is done
before crushing in BSP.
Importance of Crushing:
Fine crushing of coal is essential to homogenize the different inherent constituents of
coal otherwise the coke produced will have different coking behaviour depending on
its original coal structure. Crushing of coal is done by hammer crusher. Crushing also
adds to improve the bulk density of coal charge in the ovens. Bulk density is the
compactness or close packing of the coal charge in the oven. Higher the bulk density
better is the coke strength. Bulk density can also be increased by addition of
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briquettes. This facility exists in RSP & BSP only. It has been observed that the
same coal blend, after crushed to a fineness of 70% against the normal requirement of
82%, will result in deterioration in strength, denoted as M-10, by 1.5% to 2.0%. It is
desirable to have 80% to 82% of - 3.2mm size coal after crushing. This is known as
crushing Index. However over crushing is not desirable as this reduces the bulk
density & increases micro fines, which causes problem in battery operation.
Importance of Blending:
Blending plays a vital role in producing good metallurgical coke. Blending is a
process of mixing the different types of coal, i.e. PCC, MCC, Soft & Hard, in a
predetermined ratio to reduce the ash percentage of the blend coal, keeping the other
coking properties intact. As evidenced from the table under properties of coal the
Indigenous coals contain a relatively higher percentage of ash & Imported coals
contain a relatively lower percentage of ash. Hence a proper mixing, i.e. blending of
both types of coal is necessary.
However, blending is to be done in a very accurate manner so that required coke
property does not get adversely affected. Blending is generally done by adjusting the
discharge of different types of coal from bunkers or silos to a common belt. The
different type of coals gets thoroughly mixed during crushing where blending is done
before crushing. In case where blending is done after crushing proper mixing takes
place at several transfer points, i.e. during discharge from one conveyor to another
conveyor through a chute, during transportation to coal towers or service bunkers.
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4 BLAST FURNACE
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4.1 Introduction
BF is a counter current heat and mass exchanger, in which solid raw materials are charged
from the top of the furnace and hot blast, is sent through the bottom via tuyeres. The heat is
transferred from the gas to the burden and oxygen from the burden to the gas. Gas ascends up
the furnace while burden and coke descend down through the furnace. The counter current
nature of the reactions makes the overall process an extremely efficient one in reducing
atmosphere. The real growth of blast furnace technology came with the production of high
strength coke which enabled the construction of large size blast furnaces.
The raw materials and their quality:
In India steel is being produced largely through the blast furnace/ B.O.F.route. Iron ore, sinter
and coke are the major raw materials for blast furnace smelting.
The following raw materials used for the production of pig iron: -
(i)Iron ore (ii) Limestone (iii) Dolomite (iv) Quartzite (v) Manganese ore (vi) Sinter.
Iron ore: Iron bearing materials; provides iron to the hot metal. It is the principal mineral in
blast furnace for extraction of pig iron; generally rich in iron content varying from 60% to
66%. The high alumina content makes the slag highly viscous and creates problems for stable
furnace operation.
Limestone: Acts as flux. Helps in reducing the melting point of gangue present in the iron
bearing material and combines effectively with acidic impurities to form slag in iron making.
Quartzite: Acts as an additive quartzite is a mineral of sio2 (silica) and under normal
circumstances contains about 96-97% of sio2 rest being impurities.
Manganese ore: Acts as additive for the supply of Mn in the hot metal. Mn ore is available
in the form of combined oxides of Mn and Fe and content of Mn is about 31- 32% for steel
plant use
Coke: Acts as a reductant and fuel supports the burden and helps in maintaining permeable
bed
Sinter: It is iron bearing material. Sintering is the process of agglomeration of fines (steel
plant waste) by incipient fusion caused by heat available from the fuel contained in the
charge. The lumpy porous mass thus available / obtained is known as “sinter”
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Coal dust: Acts as an auxiliary fuel, reduces coke consumption in the BF
Coal tar: Acts as an auxiliary fuel, reduces coke consumption in the BF
4.2 Blast Furnace and Accessories
Blast furnace is basically a counter current apparatus, composed of two truncated cones
placed base to base.
The sections from top down are
Throat, where the burden surface is.
The shaft or stack, where the ores are heated and reduction starts.
The bosh parallel or belly and
The bosh, where the reduction is completed and the ores are melted down.
The hearth, where the molten material is collected and is cast via the tap hole.
4.3 Zones in Blast Furnace
UPPER STACK ZONE
Reduction of Oxides
Decomposition of Hydrates
Water - Gas Shift Reaction
Carbon Deposition
Decomposition of Carbonates
MIDDLE STACK ZONE
Direct/Indirect Reduction
Gas utilization
LOWER STACK ZONE
Calcinations of Limestone
Reduction of Various elements
Reduction of unreduced Iron
Reduction of Silicon
Reduction of Mn, P, Zn etc.
Formation / melting of slag,
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Final reduction of FeO and melting of Fe
COMBUSTION ZONE
Burning and combustion of Coke
Complete reduction of Iron Oxide
RACEWAY
Coke and Hydrocarbons are oxidized
Large evolution of heat
HEARTH
Saturation of Carbon with Iron
Final Reduction of P, Mn, Si and Sulphur
Reaction impurities reach their final concentrations
Falling/drop of Metal and Slag bring heat down into the Hearth.
4.4 Hot Blast SectionStoves are refractory heat exchangers, through which hot products of combustion of BFG
(blast furnace gas) and blast air flow alternately for specified periods. The refractory mass,
called checker works, retains the heat from the hot flue gases thereby cooling the flue gases
in one cycle, called gas cycle; while it gives the retained heat to the cold blast in the next
cycle, called blast cycle, thereby transforming the cold blast to hot blast.
The function of Hot blast stove is to preheat the air before admission into the furnace through
tuyere. Air is preheated to temperatures between 1,000 and 1,250°c in the hot blast stoves.
Air preheated to temperatures between 1,000 and 1,250°c is produced in the hot blast stoves
and is delivered to the furnace via a hot blast main, bustle pipe and finally through the
tuyeres. The hot blast reacts with coke and injectants, forming the so-called raceway in front
of the tuyeres. There are 3 or 4 stoves for each furnace. Each stove consists of a combustion
chamber and refractory checker brickwork.
There are two cycles in the stove operation.
1. On gas: stove in the heating mode
2. On blast: stove in the blast mode
In the first cycle the stoves are getting heated by using bf gas and/or coke oven gas for 2 hrs.
The flue gases will be carried out through the chimney. This is called ‘on gases. When the
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dome temperature reaches to the desired level the gas is stopped and cold blast that is
coming from the power and blowing station is sent thorough the cold blast valve. In this
cycle called ‘on blast’ the sensible heat that is stored the checker brickwork is carried away
by the cold blast and is getting heated. Thus hot blast is produced and this blast is sent into
the blast furnace via hot blast main, bustle pipe, compensator, tuyeres stock and tuyeres. ‘On
blast’ will continue for one hour and will be followed by “on gas’ cycle. Thus at any point of
time two stoves are ‘on gas’ and one or two stoves are ‘on blast’ and the cycle is repeated
continuously. Heated stove kept isolated, as ready for on blast cycle
The hot blast is delivered to the furnace via a hot blast main, bustle pipe and finally through
the tuyeres. The hot blast reacts with coke and injectants, forming a cavity, called raceway in
front of the tuyeres.
A snort valve on the cold blast main regulates the volume of blast. The steam is injected for
the humidification of the blast before pre-heating in the stove. Oxygen enrichment is also
done whenever necessary through the blast itself. A mixer valve regulates hot blast
temperature.
4.5 CAST HOUSE
Function
The function of cast house is to tap the liquid metal and slag via the tap hole from hearth on
scheduled time and separate the metal and slag in trough which is made up of refractory mass
by skimmer block and direct metal to metal ladles and slag to the slag ladles or CHSGP.
Process and parts of cast house:
In the BF of single tap hole, there is a provision to flush the slag through the slag notch
(called monkey) situated at a height of 1400 mm - 1600 mm from the axis of the tap hole.
The monkey is equipped with pneumatic or manual cinder stopper. Increasing the number of
toppings can reduce flushing operation.
Cast house consist of tap hole, trough, iron and slag runners and their spouts and various
equipments. The hot metal is tapped out at an interval of 1-2 hrs depending upon the furnace
condition. The tapping time will be around 90 – 120 minutes. Generally 8 -9 tapings will be
done in a day. The usual way of opening the tap hole is to drill the tap hole until the skull is
reached. Sometimes oxygen lancing is carried out to melt the skull. Generally the tap hole is
located in such a way that after tapping minimum amount of metal should remain in the
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hearth. So it is almost at the bottom most part of the hearth. After opening the tapping hot
metal will comes out first. After some time the liquid level in the hearth decreases and the
slag that will be floating on the metal comes out of the tap hole. The skimmer plate separates
the slag from the metal and diverts the slag into the slag ladles/SGP through slag runners. The
hot metal continues to flow down the bend runner from which it is diverted into individual
metal ladles. The control of this operation is accomplished by cutters located in the runners or
with the help of rocking runner and pusher car. At the end of the tapping the tap hole is
closed with the mud gun, which is electrically or hydraulically operated
The hot metal is collected in a refractory lined vessel called hot metal ladle and for safety
reasons it is filled up to 85-90%. Using these ladles hot metal is transported from blast
furnace to mixers in SMS, PCM and foundry. Similarly slag is collected in slag ladles and is
dumped in the dump post or sends to slag granulation plants (SGPs) in which slag is
granulated, and this granulated slag is sold to cement manufacturers.
The equipments available at the cast house are:
1. Drill machine - Hydro-pneumatic or electric drilling machines are used for opening the
tapping
2. Mud gun - Hydraulic or electric drilling machines are used for closing the tapping with
anhydrous or water bonded tap hole mass
3. Cast house crane - for material handling during cast house preparation
4. Rocking runner - to divert the metal into a different metal ladle (tilting runner)
5. Pusher car - used for local placement of the metal ladle
Auxiliary sections:
The auxiliary section of blast furnace consists of following sections:
1. Ladle repair shop 2. Pig casting machine
Ladle repair shop: ladle repair shops provided for relining, repairing and cleaning of
the iron ladles. Shop contains E O T. cranes for speeding up the job.
Pig casting machine: there is double strand pig casting machines. Each machine
contains no. of moulds in one belt with lime coating arrangement underneath the machine.
Moulds are filled with the hot metal from the ladle at the spout, cooled by water sprays on the
bed while on movement and the pigs are separated from mould chain by knockout
arrangement.
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Equipments of PCM
WINCH- to lift the loaded liquid metal ladle.
TWO STANDS- (frames) to hold the ladle firmly, with the paws attached in both the
sides of the ladle.
RUNNER- to receive the liquid metal and to pour into the moulds through spouts.
LIME SPRAY UNITS- to make a thick coating of lime on the moulds to avoid
sticking of cold metal with the moulds.
Tap hole mass shop: here, refractory mass required for blast furnace department is made and
stored e.g. mud gun clay, tap hole frame mass and runner mass etc...
Auxiliary fuel injection
In the present competitive environment, there is a lot of pressure on bf operators to lower the
operating costs and maximize productivity. One way to achieve this is by injecting auxiliary
fuel into the blast furnace. The fuels used for this purpose are pulverized coal, and coal tar.
The challenge now is to achieve high PCI rates with cheaper, lower quality raw materials,
without losing hot metal quality, productivity or bf availability.
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5 STEEL MAKING
5.1 Introduction
The Hot Metal, which is produced by Blast Furnaces, consists of various impurities. Main
impurity present is Carbon and other impurities like phosphorus, sulphur, silicon, non-
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metallic inclusions etc are also present. Steel making is the process of purification of this
Hot Metal. Steel such produced is the pure form of metal. Hot Metal contains around 4%
of Carbon, which is reduced below 0.1% as per the requirement. Other impurities like
sulphur, phosphorus are removed and alloying elements such as manganese, nickel,
chromium and vanadium are added to produce the exact steel required. The various processes
involved in steel making are as follows.
HMDS—HOT METAL DESULPHURISATION
BOF—BASIC OXYGEN FURNACE
OH/TH—OPEN HEARTH/TWIN HEARTH
ARS—ARGON RINSING STATION
LF—LADLE FURNACE
RH DEGASSER—RUHR –STAHL HERAUS (Process is named on a German town and a
German scientist)
VAD—VACCUM ARC DEGASSER
VOD—VACCUM OXYGEN DECARBURISATION
CCS/CCP—CONTINUOUS CASTING SHOP/ PLANT
5.2 HOT METAL DESULPHURISATION
Sulphur is mainly present in the iron ore and in the coal. Reducing the sulphur content to less
than 0.020% in the blast furnace is difficult from an economical standpoint. As the steel
quality often requires a sulphur content of 0.010%, the hot metal must be de-sulphurised in
another way. In desulphurization methods alone lime, or magnesium reagent, and calcium
carbide may be used in proper proportion. They are injected into the metal with special
designed lances under a gaseous stream. In this way, the sulphur content can be reduced to
levels below 0.005 %. Hot metal in a ladle brings to Desulphurization unit by EOT cranes or
rail. After proper positioning of the ladle, injection lance is lowered deep into the metal. Then
start injection of the said material through the lance and is continued for 5 to 10 minutes
depending upon sulphur content in hot metal . Ladle is then taken to slag racking machine to
remove the slag formed during the injection process. Hot metal is then sent to converter.
5.3 OPEN /TWIN HEARTH FURNACES
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One of the oldest established process of steel making, most open hearth furnaces were
closed by early 1990’s, because of their fuel inefficiency, low productivity and
cumbersome operation. Basic oxygen steel making (BOF) or LD process replaced open
hearth furnaces. In SAIL modified form of Open hearth furnace is still in operation called
Twin Hearth Furnace.
Twin hearth furnace consists of two hearths separated by a bridge wall with a common roof.
Twin hearth furnace works on synchronization between the two hearths, there by both the
hearths are engaged in different operations. While one is in solid period, the other will be in
liquid period.
The fundamental principle of Twin Hearth Furnace is physical and chemical heat generated
during blowing in one hearth is utilized in the adjoining hearth for preheating the charge,
making the process faster. The tap-to-tap time of THF is cut by half since the furnace is
tapped from both the hearth alternatively at an interval of one half of the heat duration in one
hearth. Operational efficiency of the furnace is based on the equal duration of the both cold
and hot period i.e. in one hearth when melting starts the other hearth must be tapped.
5.4 BASIC OXYGEN FURNACE (BOF)- LD CONVERTER
Basic Oxygen Furnace is commonly known as BOF process or LD process. As compared to
open / twin hearth process is fast, energy efficient and simple. Tap to tap time in BOF is
around 45-50 minutes. The name BOF Stands B mean basic because basic refractory is used,
O means oxygen as it is blown in converter and F means furnace.
Inputs: The major input materials in BOF or LD converter are:
Metallic: Hot metal containing around 4% carbon is the main input in the BOF. Scrap
is also used as a coolant and is also used in the process.
Fluxes: Fluxes such as lime, dolomite, iron ore etc.
Oxygen: one of the important inputs comes mainly from captive Oxygen plants in
addition to the Purchased liquid oxygen. Oxygen Purity should be more than 99.0%.
Nitrogen: Nitrogen is used for purging and ceiling purpose. It is also used for slag
splashing.
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Ferro-Alloys: while tapping the steel Ferro-alloy such as ferro silicon (Fe- Si),
silico manganese (Si-Mn), ferro manganese (Fe-Mn) etc are being added to make
the desired grade of steel.
Process:
Charging: The process start with mixer in steel melting shop. Metal is stored in
Mixers and it is taken out as and when needed. It is charged into converter with the
help of EOT cranes. In addition to metal, scrap is also charged. Charging sequence
followed in BOF is first scrap and then metal.
Converter blowing: The process of blowing means reaction of Oxygen with hot
metal and fluxes in LD converter. After charging converter is kept vertical and lance
is lowered in the converter through which oxygen is blown at a pressure of around 14
kg/cm2. During the blowing process fluxes such lime, dolomite, iron ore etc are added
to make slag. The slag is basic in nature. Main impurities carbon reacts with oxygen
and is removed in the gaseous form. Impurities like Si, P, S and other non metallic
impurities are removed in the form of slag. The blowing process usually takes 17
mins. When the blowing is complete converter is tilted to take out the slag in a slag
pot. Sample and temperature is also taken manually. When desired composition and
temperature is achieved the steel is tapped.
Tapping: tapping means discharging the liquid steel into ladle through the tap hole
present in the converter by tilting it. As per the grade of steel the Ferro-alloys are also
added into ladle during tapping. As soon as the steel finishes the converter is lifted
and tapping is complete.
Nitrogen Slashing: After tapping, the residual slag in the converter issplashed with
the help of nitrogen. Converter is kept vertical and lance is lowered. Through the
same lance nitrogen is blown which splashes the basic residual slag in the converter
and gives a coating on the refractory bricks. Main advantage of nitrogen splashing is
to increase the lining life of the converter.
Refractories
Refractory plays a very important role in BOF shop. As liquid metal is handled in BOF
so all vessels like mixer, converter, ladles etc are lined with refractory bricks. It protects
the shell of vessel and retains the metal temperature. Different types of refractory as per
their usage are given below:
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Converter Vessel: The bricks used here are basic in nature. Dolomite bricks or
magnesia carbon bricks are commonly used in converter. In recent times magnesia
carbon bricks have replaced dolomite bricks. Number of heats made in a converter
from one new lining to next lining is known as the lining life of the converter. Now a
day’s all plants are trying to achieve higher lining life.
Equipments
Major equipments in BOF shop are:
Converter: A converter is an open pear shaped vessel made of steel and lined from
inside with basic refractory bricks. It can be rotated through 3600. Charging and de-
slagging is done through mouth where as tapping of steel is done through a hole
called tap hole.
Lance: It is made of three concentric steel tubes to circulate water around the centre
tube and pass oxygen through the innermost tube. Its tip is made of copper. Always a
stand by lance is provided in a converter.
Gas Cleaning Plant: A huge quantity of waste gases containing dust particles
generated during the process is passed through the GCP. Primarily water is sprayed
over the gases to separate the solid particles. Cleaned gases are either collected in a
gas holder or burnt in the atmosphere to control air pollution.
Safety Aspects
As we deal with liquid metal in the Shop personal as well as equipment safety is of
large concern. We should strictly follow the safety norms.
Before charging, it should be ensured that no liquid slag is left in the converter. It
should be dried by adding lime.
There should not be any water in the slag pot in which the slag is dumped.
Persons working in the steel melting shop should use personal protective equipment
i.e. gloves, blue glass, fire retarding jackets.
Blowing should not be done if there is any water leakage in the lance.
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6 CASTING
6.1 Introduction
In modern steel plants everywhere there is a demand for more and more quality finished
products. For rolling to very thinner products, continuous casting products are the best
compared to teeming of the steel to make ingots and then to roll the ingots to produce slabs or
billets or blooms. Continuous casting not only meets the higher production within same time
frame but the quality of such products is quite lucrative and hence demanding.
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Liquid steel comes from the ladle into the tundish. Tundish is a device where it collects,
accumulates liquid steel from the ladle and feeds to two or more moulds through SEN
depending on the m/c and process.
The basic design of the caster is to solidify liquid steel to its solid products
uninterruptedly/continuously. For that the steel to be cast must be killed. Steel from which
oxygen (dissolved in steel during steel making in BOF) is removed at SRU using highly
deoxygenating elements like Al (Aluminum) Si (silicon) etc is called KILLED STEEL.
Oxygen in steel is measured using Celox Temp and expressed in ppm. Steel that is to be cast
should not have high ppm of O2 otherwise casting cannot be done because O2 of steel will
form unwanted oxides viz CaO, SiO2, MgO and will be deposited over the entry nozzle and
thus will restrict the flow of steel into the mould.
6.2 Casting Preparation
1. Steel that is to be cast is treated well at SRU for smooth casting.
2. Tundish through which casting will be done is to be prepared.
Tundish is a device through which continuity of the casting is maintained. There are two
types of casting practices are in use namely cold tundish and hot tundish practices. Liquid
steel comes from the ladle into the tundish and in turn the tundish feeds the liquid steel into
the mould through different outlet at the bottom of the tundish. Tundish is made of steel and
inside of which is lined with refractory bricks or castable. After that tundish boards are fixed
over the refractory lined. Submerged entry nozzle (SEN) are fixed by clamping device in
each of the tundish outlet.
3. Preparing of the mould:
Mould is the most important equipment in the caster m/c. primarily mould is prepared
according to the shape and size of the product. For solidification of the initial liquid steel that
enters into the mould one DUMMY BAR head is used, which is fed into the mould with a
fixed rod or flexible chain. This DUMMY BAR head is packed. Mould is made purely of
copper as copper has the most heat discharge capacity than any other metal economically
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available. All sides of this mould is made up of Cu plate and heat from liquid steel
immediately discharges trough the copper plates by mould cooling system Copper plates
are cooled by circulating soft water through designed tubes in the form of coils. Here the
difference of MOULD COOLING WATER Outlet Temperature & Inlet Temperature is
monitored continuously. It is very much hazardous part in caster m/c during casting. An
alarm is provided as soon as the difference of temperature raises more. Immediate actions are
to be taken and if necessary casting should be stopped without waiting for any other decision
to be asked from anyone.
6.3 Casting Process
Liquid steel taken into ladle is refined at SRU is placed over the turret arm and ladle SG is
fixed. Then one shroud is fixed at the bottom of the ladle collector nozzle so that no stream of
liquid steel comes in contact with the atmosphere and no spillage occurs. This liquid steel
gradually fills the tundish and from there liquid steel leaves tundish nozzle/TSG through SEN
into the mould. Initially steel rests on the DUMMY BAR head on which some chillers are
placed to get the liquid steel freeze/solidifies quickly then the m/c starts with MOM & casting
powder is to be sprayed continuously at a certain mould level. The process continues after the
DUMMY BAR head is disconnected as it reaches at its particular position. Length of the
slab/billet is maintained by using cutting torch/ shearing blades.
Abnormalities:
During casting and form some unwanted hard oxides, which gets deposited over the steel into
the mould and interrupts the steel flow. Sometimes casting is to be aborted due to this flow
restriction. This phenomenon is called Chocking. In some cases temperature at which liquid
steel gets solidified may be reached during casting, which caused solidification at SEN and
restricts the steel flow, and then also casting continuity gets disturbed and casting stops. This
is called Freezing. So during fixing of the SEN proper care should be taken.
Another major problem that hinders the casting process is Break Out.
Some Casting Defects:
Types of defects:
• Surface cracks
• Internal cracks
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• Blow holes, Pin holes etc
Remedial measures:
• Control of superheat of liquid steel (appropriate temperature)
• Steel chemistry
• Casting speed
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7 OTHER FACILITIES
7.1 Steel Melting Shops
Hot Metal from the Blast Furnaces is converted into steel by blowing 99.5% pure Oxygen through it in the LD converter. Suitable alloying elements are added to produce different grades of steel.
Bokaro has two Steel Melting Shops - SMS-I and SMS-II. SMS-I has 5 LD converters of 130T capacity each. It is capable of producing Rimming steel through the ingot route. SMS-II has 2 LD converters, each of 300 T capacities, with suppressed combustion system and Continuous Casting facility. It produces various Killed and Semi-Killed steels.
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7.2 Continuous Casting Shop
The Continuous Casting Shop has two double-strand slab casting machines, producing high quality slabs of width ranging from 950 mm to 1850 mm. CCS has a Ladle Furnace and a Ladle Rinsing Station for secondary refining of the steel. The Ladle Furnace is used for homogenizing the chemistry and temperature. The concast machines have straight moulds, unique in the country, to produce internally clean slabs.
CCS produces steel of Drawing, Deep Drawing, Extra Deep Drawing, Boiler and Tin Plate quality. It also produces low alloy steels like LPG, WTCR, SAILCOR and API Grade.
7.3 Slabbing Mill
Slabbing Mill transforms ingots into slabs by rolling them in its 1250 mm Universal Four-High Mill. The rolling capacity of the Mill is 4 MT per annum. The shop has Hot and Cold Scarfing Machines and 2800 T Shearing Machine. Controlled heating in Soaking Pits, close dimensional accuracy during rolling and hot and cold scarfing help produce defect-free slabs.
7.4 Hot Strip Mill
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Slabs from CCS and Slabbing Mill are processed in the state-of-the-art Hot Strip Mill. The fully automatic Hot Strip Mill with an annual capacity of 3.363 million tonnes has a wide range of products - thickness varying from 1.2 mm to 20 mm and width from 750 mm to 1850 mm. The mill is equipped with state-of-the-art automation and controls, using advanced systems for process optimization with on-line real time computer control, PLCs and technological control systems.
Hot Rolled Coil Finishing
All the Hot Rolled coils from the Hot Strip Mill are received in HRCF for further distribution or dispatch. HR Coils rolled against direct shipment orders are sheared and finished to customer-required sizes and dispatched to customers. The material is supplied as per Indian specifications and many international/ foreign specifications. The shop has two shearing lines
with capacities of 6, 45,000 Tonnes/ year and 4, 75,000 Tonnes/ year respectively.
7.5 Cold Rolling Mill
The Cold Rolling Mill at Bokaro uses state-of-the-art technology to produce high quality sheet gauge material, Tin Mill Black Plate and Galvanized Products. Cold rolling is done to produce thinner gauge strips of very smooth and dense finish, with better mechanical properties than hot rolling strips.
Hot Dip Galvanizing Complex
The Hot Dip Galvanizing Complex integrated with the CRM produces zinc-coated Cold Rolled strips resistant to atmospheric, liquid and soil corrosion The first shop of Bokaro Steel to get the ISO 9001certification way back in 1994, this complex
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has maintained a high-standard of coating quality and its SAILJYOTI branded products enjoy a loyal market. This complex made certain innovations for higher productivity to help re-build earthquake ravaged Gujarat.
7.6 BOKARO STEEL PLANT - PRODUCT BASKETMill Capabilities
Shop Products Facility Annual
Capacit
y (,000
Tones)
Thickness
range
(mm)
Width
range
(mm)
Length
(meter)
HSM HR Coils/ Sheets/
Plates
Continuous
Mill
3955 1.6 -16 900-
1850
HRC
F
HR Sheets/ Plates Shearing Line-
I
- 5-10 1800 2.5-12
HR Sheets/ Plates Shearing Line-
II
1.6-4 1500 1.5-4.5
HR Coil Slitting Line
CRM 1660
CR Coils/ Sheets CRM-I
complex
0.63-2.5 700-
1850
CR Coils/ Sheets CRM-II
complex
0.63-1.6 650-
1250
CR Coils/ Sheets,
TMBP
DCR Mill 100 0.22-0.8 650-
1040
GP Coils & Sheets
GC Sheets
HDGL 170 0.3-1.6 650-
1250
By Products
Nitration-grade Benzene
Nitration-grade Toluene
Light Solvent Naphtha
Still Bottom Oil
Hot Pressed Naphthalene
Anthracene Oil
Extra-hard Pitch
Hard-medium Pitch (solid/
liquid)
Ammonium Sulphate
Pitch Creosote
Mixture
BF Granulated Slag
Liquid Nitrogen
Phenol Fraction
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